To assess the effective and safe protocols in ovulation induction by gonadotropin therapy, we studied on 3 protocols, (1) conventional FSH therapy (FSH therapy), (2) low dose FSH therapy (LD-FSH therapy) and (3) sequential FSH and pulsatile GnRH treatment (FSH-GnRH treatment) for 2 patient group with hypothalamic anovulation (HA) and Polycystic ovary syndrome (PCOS).The mean treatment period in FSH-GnRH therapy is not changed with that of FSH therapy, but that of LD-FSH therapy is longer than other groups. The mean numbers of follicles are FSH therapy >LD-FSH thepy>GSH-GnRH therapy. The incidences of single folliculogenesis per treatment cycle by FSH-GnRH therapy were 70% in HA and 50% in PCOS.No significant differences were observed among 3 groups in the incidences of oulation and pregnency. We did not observe multiple pregnancy in LD-FSH therapy and FSH-GnRH therapy. The incidences of ovarian stimulation syndrome (OHSS) were FSH therapy>LD-FSH thepy>GSH-GnRH therapy. Especially, that in FSH-GnRH therapy was significantly lower than those in other groupsThese data suggested that LD-FSH therapy is a effective and safe protocol of gonadotropin therapy because it reduces the side effects of gonadotropin therapy, multiple pregnancy and OHSS.However, treatment periods is longer and the incidences of side effects in PCOS patients were higher than those in FSH-GnRH therapy. On the other hand, FSH-GnRH therapy is best protocol of gonadotropin treatment for reducing side effects.In conclusion of this study, LD-FSH therapy is a suitable protocol of gonadotropin treatment for low risk anovulation as HA, and FSH-GnRH therapy is best protocol for high risk patients.